1. const rafInterval = (fn, delay = 16, count) => {
    2.   let lastRunTime
    3.   let timerId = null
    4.   let runCount = 0
    5.   const loop = (timestamp) => {
    6.     if (lastRunTime === undefined) {
    7.       lastRunTime = timestamp
    8.     }
    9.     timerId = requestAnimationFrame(loop)
    10.     if (timestamp - lastRunTime >= delay) {
    11.       if (count && runCount >= count) {
    12.         cancelAnimationFrame(timerId)
    13.       } else {
    14.         runCount++
    15.         fn(timestamp)
    16.         lastRunTime = timestamp
    17.       }
    18.     }
    19.   }
    20.   timerId = requestAnimationFrame(loop)
    21.   return timerId
    22. }
    24. let id
    25. let count = 0
    26. let b = (t) => {
    27.   console.log(count, t)
    28.   count++
    29.   id = rafInterval(b, 2000, 1)
    30.   if (count > 8) {
    31.     window.cancelAnimationFrame(id)
    32.   }
    33. }
    34. b()